As the demand for high power and high energy density of a lithium secondary battery continues to rise, more and more research units are dedicated to increasing the safety and the stability of the lithium secondary battery. Moreover, since the dependence on portable electronic products is increased, and applications of an electrochemical energy storage apparatus in, for instance, automobiles and uninterruptible power supplies are expected to increase, the requirements for the safety of the lithium secondary battery need to be further improved, in particular when the lithium secondary battery is applied in, for instance, airplanes of high-altitude flight or space shuttles. Currently, research related to safety is often focused on the development of, for instance, a flame retardant additive, solid electrolyte, or a new electrolyte system, so as to alleviate various issues of the liquid electrolyte and increase the thermal stability of the electrochemical energy storage device. Moreover, it is desired to effectively reduce or completely omit an organic solvent having high volatility and flammability.
The polyelectrolyte in the solid electrolyte is also called a single-ion conductor (SIC), and an anion or a cation of the polyelectrolyte is covalently bonded on the repeating unit of a polymer. Since the anion or the cation is fixed on a polymer chain, the ion does not cause a concentration gradient. As a result, the possibility of a salt being deposited on an electrode or a separator is reduced, such that cycle life of the device is extended.
Although the polyelectrolyte can inhibit puncture by the deposit of lithium metal, thus increasing the safety of the lithium battery, and the polyelectrolyte can be arbitrarily prepared in terms of size and shape and is suitable for various lithium batteries, the worse ionic conductivity (solid polymer electrolyte is about 10−5 S/cm, single ion conductor is about 10−6 S/cm) thereof has always hindered its application and commercialization.